User terminal, cellular base station, and processor

ABSTRACT

A user terminal, method, and apparatus receive an offload command instructing an offload from a cellular base station, the offload steering traffic from the cellular base station to a wireless local area network (WLAN) access point being while maintaining a connection between the user terminal and cellular base station. An attempt is made to connect to the WLAN access point in response to receiving the offload command, and in response to the attempt failing, determine whether a reason for the failure of connection to the WLAN access point is a first reason being an issue of a radio link between the user terminal and the WLAN access point or a second reason being an internal issue of the user terminal. A failure indication is transmitted to the base station in response to a connection failure indicates connection failure and indicates whether the reason is the first or second reason.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation Application of U.S. patentapplication Ser. No. 15/197,837 filed Jun. 30, 2016, which is aContinuation Application of U.S. patent application Ser. No. 14/906,760filed Jan. 21, 2016 which is the U.S. National Phase Application ofInternational Patent Application No. PCT/JP2014/070530 filed Aug. 4,2014, which claims benefit of Japanese Patent Application No.2013-164056 filed Aug. 7, 2013 the entire contents of which areincorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to a user terminal used in a cellularcommunication system capable of cooperating with a wireless LAN system,a cellular base station therefor, and a processor therefor.

BACKGROUND ART

In recent years, the use of a user terminal including a cellularcommunication unit and a wireless LAN communication unit (so-called dualterminal) is widely spread. Further, the number of wireless LAN accesspoints managed by an operator of a cellular communication systemincreases.

Therefore, in 3GPP (3rd Generation Partnership Project) which is aproject aiming to standardize a cellular communication system,consideration is given to a technology capable of strengtheningcooperation between a cellular communication system and a wireless LANsystem.

For example, when traffic transmitted and received between a userterminal and a cellular base station is transitioned to a wireless LANsystem, it is possible to reduce the traffic load of the cellular basestation (offload).

As a method of performing such an offload, there is proposed a method inwhich the cellular base station sets a WLAN measurement to a userterminal subject to offload, the user terminal reports a WLANmeasurement result to the cellular base station, and then the cellularbase station transmits an offload command to the user terminal on thebasis of the report (see Non Patent Literature 1).

CITATION LIST Non Patent Literature

[NPL 1] 3GPP technical report “TR 37.834 V0.3.0” May, 2013

SUMMARY

From the viewpoint of the cellular base station, as a method ofselecting a user terminal subject to offload, it may be possible toconsider a method in which a user terminal having a large amount ofradio resources used is selected.

However, from the viewpoint of the user terminal, when a user terminalsubject to offload is selected on the basis only on such a selectioncriterion, a preferable selection may be not performed. The offloadshould not be performed on a user terminal such as a user terminalaround which no wireless LAN access point is present, a user terminalwhich is moving, or a user terminal whose battery remaining amount issmall.

Therefore, the present disclosure provides a user terminal, methodthereof, and apparatus thereof with which it is possible to properlyselect a user terminal subject to offload.

A user terminal according to the disclosure comprises a controllerincluding at least one processor and at least one memory configured toreceive an offload command from a cellular base station. The offloadcommand instructs an offload, the offload being an operation in whichthe user terminal steers traffic from the cellular base station to awireless local area network (WLAN) access point while maintaining aconnection between the user terminal and the cellular base station. Theat least one processor and at least one memory are configured to attemptto connect to the WLAN access point in response to receiving the offloadcommand, and in response to failing in connecting to the WLAN accesspoint, determine whether a reason for the failure of connection to theWLAN access point is a first reason or a second reason. The first reasonis an issue of a radio link between the user terminal and the WLANaccess point, and the second reason is an internal issue of the userterminal. The at least one processor and at least one memory areconfigured to transmit a failure indication to the cellular base stationin response to failing in connecting to the WLAN access point. Thefailure indication indicating that the user terminal fails in connectingto the WLAN access point and includes information indicating whether thereason is the first reason or the second reason.

A method according to the disclosure for performing at a user terminalcomprises receiving an offload command from a cellular base station, theoffload command instructing an offload, the offload being an operationin which the user terminal steers traffic from the cellular base stationto a wireless local area network (WLAN) access point while maintaining aconnection between the user terminal and the cellular base station. Themethod comprises attempting to connect to the WLAN access point inresponse to receiving the offload command, and in response to failing inconnecting to the WLAN access point, determining whether a reason forthe failure of connection to the WLAN access point is a first reason ora second reason. The first reason is an issue of a radio link betweenthe user terminal and the WLAN access point, and the second reason is aninternal issue of the user terminal. The method comprises transmitting afailure indication to the cellular base station in response to failingin connecting to the WLAN access point, where the failure indicationindicates that the user terminal fails in connecting to the WLAN accesspoint. The failure indication includes information indicating whetherthe reason is the first reason or the second reason.

An apparatus according to the disclosure for controlling a user terminalcomprises at least one processor and at least one memory configured toreceive an offload command from a cellular base station, the offloadcommand instructing an offload, the offload being an operation in whichthe user terminal steers traffic from the cellular base station to awireless local area network (WLAN) access point while maintaining aconnection between the user terminal and the cellular base station. Theat least one processor and at least one memory are configured to attemptto connect to the WLAN access point in response to receiving the offloadcommand, and in response to failing in connecting to the WLAN accesspoint, determine whether a reason for the failure of connection to theWLAN access point is a first reason or a second reason. The first reasonis an issue of a radio link between the user terminal and the WLANaccess point, and the second reason is an internal issue of the userterminal. The at least one processor and at least one memory areconfigured to transmit a failure indication to the cellular base stationin response to failing in connecting to the WLAN access point, thefailure indication indicating that the user terminal fails in connectingto the WLAN access point. The failure indication includes informationindicating whether the reason is the first reason or the second reason.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a system configuration diagram according to a first embodimentand a second embodiment.

FIG. 2 is a block diagram of a UE (user terminal) according to the firstembodiment and the second embodiment.

FIG. 3 is a block diagram of an eNB (cellular base station) according tothe first embodiment and the second embodiment.

FIG. 4 is a block diagram of an AP (wireless LAN access point) accordingto the first embodiment and the second embodiment.

FIG. 5 is a protocol stack diagram of a radio interface in an LTEsystem.

FIG. 6 is a configuration diagram of a radio frame used in the LTEsystem.

FIG. 7 is a sequence diagram illustrating a basic operation according tothe first embodiment.

FIG. 8 is a sequence diagram of an operation pattern 1 according to thefirst embodiment.

FIG. 9 is a sequence diagram of an operation pattern 2 according to thefirst embodiment.

FIG. 10 is a sequence diagram of an operation pattern 3 according to thefirst embodiment.

FIG. 11 is a sequence diagram according to the second embodiment.

DESCRIPTION OF EMBODIMENTS Overview of Embodiments

A user terminal according to a first embodiment and a second embodimenttransmits and receives traffic to and from a cellular base station in acellular communication system capable of cooperating with a wireless LANsystem. The user terminal comprises a controller configured todetermine, on the basis of a determination parameter related to asituation of the user terminal, whether or not an offload in which thetraffic is transitioned to the wireless LAN system should be performed,when the user terminal is selected as a target terminal subject to theoffload. The controller transmits, to the cellular base station, arejection notification that related to rejection to the offload when thecontroller determines that the offload should not be performed.

In the first embodiment, the determination parameter is informationindicating whether or not a wireless LAN access point is present aroundthe user terminal. The controller determines that the offload should notbe performed when no wireless LAN access point is present around theuser terminal.

In the first embodiment, the determination parameter is informationindicating whether or not the user terminal is moving. The controllerdetermines that the offload should not be performed when the userterminal is moving.

In the first embodiment, the determination parameter is informationindicating a battery remaining amount of the user terminal. Thecontroller determines that the offload should not be performed when thebattery remaining amount falls below a threshold value.

In the first embodiment, the determination parameter is informationindicating a power consumption level of the user terminal. Thecontroller determines that the offload should not be performed when thepower consumption level exceeds a threshold value.

In an operation pattern 1 according to the first embodiment, the userterminal further comprises a receiver configured to receive, from thecellular base station, a wireless LAN measurement command indicatingthat the user terminal is selected as a target terminal subject to theoffload. The controller transmits the rejection notification to thecellular base station as a response to the wireless LAN measurementcommand when the controller determines that the offload should not beperformed.

In an operation pattern 2 according to the first embodiment, the userterminal further comprises a receiver configured to receive, from thecellular base station, a wireless LAN measurement command indicatingthat the user terminal is selected as a target terminal subject to theoffload. The controller transmits, to the cellular base station, therejection notification together with a wireless LAN measurement reportto report a result of the wireless LAN measurement when the controllerdetermines that the offload should not be performed.

In an operation pattern 3 according to the first embodiment, the userterminal further comprises a receiver configured to receive an offloadcommand, that instructs an execution of the offload, from the cellularbase station. The controller transmits, to the cellular base station,the rejection notification as a response to the offload command when itis determined that the offload should not be performed.

In the first embodiment, the controller includes rejection reasoninformation indicating a reason for rejection in the rejectionnotification when the rejection notification is transmitted to thecellular base station.

In the second embodiment, the user terminal further comprises atransmitter configured to transmit, to the cellular base station, aterminal information notification including the determination parameterbefore the user terminal is selected as a target terminal subject to theoffload.

A cellular base station according to the first embodiment and the secondembodiment transmits and receives traffic to and from a user terminal ina cellular communication system capable of cooperating with a wirelessLAN system. The cellular base station comprises a controller configuredto exclude the user terminal from a target terminal subject to offloadin which the traffic is transitioned to the wireless LAN system, whenthe user terminal is selected as a target terminal subject to theoffload and when the controller receives a rejection notificationrelated to rejection to the offload from the user terminal.

In the second embodiment, the cellular base further comprises a receiverconfigured to receive, from the user terminal, a terminal informationnotification including a determination parameter related to a situationof the user terminal before the user terminal is selected as a targetterminal subject to the offload. The controller selects a user terminalsubject to the offload on the basis of the determination parameter.

In the second embodiment, the determination parameter is informationindicating whether or not a wireless LAN access point is present aroundthe user terminal. The controller excludes a user terminal, around whichno wireless LAN access point is present, from a target terminal subjectto the offload.

In the second embodiment, the determination parameter is informationindicating whether or not the user terminal is moving. The controllerexcludes a user terminal which is moving, from a target terminal subjectto the offload.

In the second embodiment, the determination parameter is informationindicating a battery remaining amount of the user terminal. Thecontroller excludes a user terminal in which the battery remainingamount falls below a threshold value from a target terminal subject tothe offload.

In the second embodiment, the determination parameter is informationindicating a power consumption level of the user terminal. Thecontroller excludes a user terminal in which a power consumption levelexceeds a threshold value, from a target terminal subject to theoffload.

A processor according to the first embodiment and the second embodimentprovided in a user terminal that transmits and receives traffic to andfrom a cellular base station in a cellular communication system capableof cooperating with a wireless LAN system. The processor executes aprocess of determining, on the basis of a determination parameterrelated to a situation of the user terminal, whether or not an offloadin which the traffic is transitioned to the wireless LAN system shouldbe performed, when the user terminal is selected as a target terminalsubject to the offload; and a process of transmitting, to the cellularbase station, a rejection notification related to rejection to theoffload when it is determined that the offload should not be performed.

First Embodiment

Hereinafter, with reference to the drawing, embodiments will bedescribed in which a cellular communication system (LTE system)configured to comply with the 3GPP standards is cooperated with awireless LAN (WLAN) system.

(System Configuration)

FIG. 1 is a system configuration diagram according to first embodiment.As shown in FIG. 1, the cellular communication system includes aplurality of UEs (User Equipments) 100, E-UTRAN (Evolved UniversalTerrestrial Radio Access Network) 10, and EPC (Evolved Packet Core) 20.The E-UTRAN 10 corresponds to a radio access network. The EPC 20corresponds to a core network.

The UE 100 is a mobile radio communication device and performs radiocommunication with a cell with which a connection is established. The UE100 corresponds to the user terminal. The UE 100 is a terminal (dualterminal) that supports both cellular communication scheme and WLANcommunication scheme.

The E-UTRAN 10 includes a plurality of eNBs 200 (evolved Node-Bs). TheeNB 200 corresponds to a base station. The eNB 200 manages one or aplurality of cells and performs radio communication with the UE 100which establishes a connection with the cell of the eNB 200. It is notedthat the “cell” is used as a term indicating a minimum unit of a radiocommunication area, and is also used as a term indicating a function ofperforming radio communication with the UE 100. Further, the eNB 200 hasa radio resource management (RRM) function, a routing function of userdata, and a measurement control function for mobility control andscheduling.

The eNBs 200 are connected mutually via an X2 interface. Further, theeNB 200 is connected to MME/S-GW 500 included in the EPC 20 via an S1interface.

The EPC 20 includes a plurality of MMES (Mobility ManagementEntities)/S-GWs (Serving-Gateways) 500. The MME is a network node forperforming various mobility controls, for example, for the UE 100, andcorresponds to a controller. The S-GW is a network node that performstransfer control of user data and corresponds to a mobile switchingcenter.

The WLAN system includes a WLAN access point (WLAN AP) 300. The WLANsystem is configured to be in compliance with the IEEE 802.11 standards,for example. The WLAN AP 300 performs communication with the UE 100 in afrequency band different from a cellular frequency band (WLAN frequencyband). The WLAN AP 300 is connected to the EPC 20 via a router, and thelike.

Further, it may be also possible that the eNB 200 and the WLAN AP 300are located individually, and it may be possible that the eNB 200 andthe WLAN AP 300 are located at a same place (Collocated). As one mode ofthe “Collocated”, the eNB 200 and the WLAN AP 300 may be directlyconnected with each other through any interface of an operator.

Next, configurations of the UE 100, the eNB 200, and the WLAN AP 300will be described.

FIG. 2 is a block diagram of the UE 100. As shown in FIG. 2, the UE 100includes: antennas 101 and 102; a cellular transceiver (cellularcommunication unit) 111; a WLAN transceiver (WLAN communication unit)112; a user interface 120; a GNSS (Global Navigation Satellite System)receiver 130; a battery 140; a memory 150; and a processor 160. Thememory 150 and the processor 160 configure a control unit. The UE 100may not have the GNSS receiver 130. It is noted that the memory 150 maybe integrally formed with the processor 160, and this set (that is, achipset) may be called a processor 160′.

The antennas 101 and the cellular transceiver 111 are used fortransmitting and receiving a cellular radio signal. The cellulartransceiver 111 converts a baseband signal output from the processor 160into the cellular radio signal, and transmits the same from the antenna101. Further, the cellular transceiver 111 converts the cellular radiosignal received by the antenna 101 into the baseband signal, and outputsthe same to the processor 160.

The antennas 102 and the WLAN transceiver 112 are used for transmittingand receiving a WLAN radio signal. The WLAN transceiver 112 converts thebaseband signal output from the processor 160 into a WLAN radio signal,and transmits the same from the antenna 102. Further, the WLANtransceiver 112 converts the WLAN radio signal received by the antenna102 into a baseband signal, and outputs the same to the processor 160.

The user interface 120 is an interface with a user carrying the UE 100,and includes, for example, a display, a microphone, a speaker, andvarious buttons. Upon receipt of the input from a user, the userinterface 120 outputs a signal indicating a content of the input to theprocessor 160. The GNSS receiver 130 receives a GNSS signal in order toobtain location information indicating a geographical location of the UE100, and outputs the received signal to the processor 160. The battery140 accumulates a power to be supplied to each block of the UE 100.

The memory 150 stores a program to be executed by the processor 160 andinformation to be used for a process by the processor 160. The processor160 includes the baseband processor that performs modulation anddemodulation, and encoding and decoding on the baseband signal and a CPUthat performs various processes by executing the program stored in thememory 150. The processor 160 may further include a codec that performsencoding and decoding on sound and video signals. The processor 160executes various processes and various communication protocols describedlater.

FIG. 3 is a block diagram of the eNB 200. As shown in FIG. 3, the eNB200 includes antennas 201, a cellular transceiver 210, a networkinterface 220, a memory 230, and a processor 240. The memory 230 and theprocessor 240 configure a control unit.

The antennas 201 and the cellular transceiver 210 are used fortransmitting and receiving a cellular radio signal. The cellulartransceiver 210 converts the baseband signal output from the processor240 into the cellular radio signal, and transmits the same from theantenna 201. Furthermore, the cellular transceiver 210 converts thecellular radio signal received by the antenna 201 into the basebandsignal, and outputs the same to the processor 240.

The network interface 220 is connected to the neighboring eNB 200 via anX2 interface and is connected to the MME/S-GW 500 via the S1 interface.The network interface 220 may be used for communication with the AP 300via the EPC 20.

The memory 230 stores a program to be executed by the processor 240 andinformation to be used for a process by the processor 240. The processor240 includes the baseband processor that performs modulation anddemodulation, encoding and decoding and the like on the baseband signaland a CPU that performs various processes by executing the programstored in the memory 230. The processor 240 implements various processesand various communication protocols described later.

FIG. 4 is a block diagram of the WLAN AP 300. As shown in FIG. 4, theWLAN AP 300 includes antennas 301, a WLAN communication unit 311, anetwork interface 320, a memory 330, and a processor 340.

The antennas 301 and the WLAN communication unit 311 are used fortransmitting and receiving a WLAN radio signal. The WLAN communicationunit 311 converts a baseband signal output from the processor 340 into aWLAN radio signal and transmits the same from the antenna 301. Further,the WLAN communication unit 311 converts a WLAN radio signal received bythe antenna 301 into a baseband signal and outputs the same to theprocessor 340.

The network interface 320 is connected to the EPC 20 via a router, andthe like. Further, the network interface 320 is used for communicationwith the eNB 200 via the EPC 20.

The memory 330 stores a program executed by the processor 340 andinformation used for a process by the processor 340. The processor 340includes a baseband processor that performs modulation and demodulation,encoding and decoding, and the like on a baseband signal and a CPU thatperforms various processes by executing a program stored in the memory330.

FIG. 5 is a protocol stack diagram of a radio interface in the cellularsystem. As shown in FIG. 5, the radio interface protocol is classifiedinto a layer 1 to a layer 3 of an OSI reference model, wherein the layer1 is a physical (PHY) layer. The layer 2 includes a MAC (Media AccessControl) layer, an RLC (Radio Link Control) layer, and a PDCP (PacketData Convergence Protocol) layer. The layer 3 includes an RRC (RadioResource Control) layer.

The PHY layer performs encoding and decoding, modulation anddemodulation, antenna mapping and demapping, and resource mapping anddemapping. Between the PHY layer of the UE 100 and the PHY layer of theeNB 200, data is transmitted via the physical channel.

The MAC layer performs priority control of data, and a retransmissionprocess and the like by hybrid ARQ (HARQ). Between the MAC layer of theUE 100 and the MAC layer of the eNB 200, data is transmitted via atransport channel. The MAC layer of the eNB 200 includes a scheduler fordetermining a transport format (a transport block size, a modulation andcoding scheme and the like) of an uplink and a downlink, and anallocated resource block.

The RLC layer transmits data to an RLC layer of a reception side byusing the functions of the MAC layer and the PHY layer. Between the RLClayer of the UE 100 and the RLC layer of the eNB 200, data istransmitted via a logical channel.

The PDCP layer performs header compression and decompression, andencryption and decryption.

The RRC layer is defined only in a control plane. Between the RRC layerof the UE 100 and the RRC layer of the eNB 200, a control message (anRRC message) for various types of setting is transmitted. The RRC layercontrols the logical channel, the transport channel, and the physicalchannel in response to establishment, re-establishment, and release of aradio bearer. When there is a connection (RRC connection) between theRRC of the UE 100 and the RRC of the eNB 200, the UE 100 is in aconnected state (RRC connected state), otherwise, the UE 100 is in anidle state (RRC idle state).

A NAS (Non-Access Stratum) layer positioned above the RRC layer performssession management or mobility management, for example.

FIG. 6 is a configuration diagram of a radio frame used in the LTEsystem. In the LTE system, OFDMA (Orthogonal Frequency Division MultipleAccess) is applied to a downlink, and SC-FDMA (Single Carrier FrequencyDivision Multiple Access) is applied to an uplink, respectively.

As shown in FIG. 6, the radio frame is configured by 10 subframesarranged in a time direction, wherein each subframe is configured by twoslots arranged in the time direction. Each subframe has a length of 1 msand each slot has a length of 0.5 ms. Each subframe includes a pluralityof resource blocks (RBs) in a frequency direction, and a plurality ofsymbols in the time direction. The resource block includes a pluralityof subcarriers in the frequency direction.

Among radio resources allocated to the UE 100, a frequency resource canbe designated by a resource block and a time resource can be designatedby a subframe (or slot).

In the downlink, an interval of several symbols at the head of eachsubframe is a control region mainly used as a physical downlink controlchannel (PDCCH). Furthermore, the remaining interval of each subframe isa region that can be mainly used as a physical downlink shared channel(PDSCH). Furthermore, in the downlink, reference signals such ascell-specific reference signals are distributed and arranged in eachsubframe.

In the uplink, both ends, in the frequency direction, of each subframeare control regions mainly used as a physical uplink control channel(PUCCH). Furthermore, the center portion, in the frequency direction, ofeach subframe is a region that can be mainly used as a physical uplinkshared channel (PUSCH).

Operation According to First Embodiment

Next, an operation according to the first embodiment will be described.

(1) Operation Overview

In the first embodiment, an operation environment is assumed in whichthe WLAN AP 300 is provided in the coverage area of the eNB 200. TheWLAN AP 300 is an AP managed by an operator (Operator controlled AP).When the eNB 200 establishes a connection with a large number of UEs100, the traffic load of the eNB 200 increases. Thus, it is possible toreduce the traffic load of the eNB 200 when traffic (user data)transmitted and received between the UE 100 and the eNB 200 istransitioned to the WLAN system (offload).

In the first embodiment, in order to perform such an offload, the eNB200 sets a WLAN measurement to the UE 100 subject to offload, the UE 100reports a WLAN measurement result to the eNB 200, and the eNB 200transmits an offload command to the UE 100 on the basis of the report.

FIG. 7 is a sequence diagram illustrating a basic operation according tothe first embodiment. In an initial state of the sequence, the UE 100 isin a state where an RRC connection is established with the eNB 200 (in aconnected state).

As shown in FIG. 7, in step S1, the eNB 200 transmits, to the UE 100subject to offload, a WLAN measurement command to control a WLANmeasurement. The WLAN measurement command includes an identifier of theWLAN AP 300 (WLAN identifier) to be measured by the UE 100. Further, theWLAN measurement command includes trigger information indicating atrigger by which a WLAN measurement report for reporting a result of theWLAN measurement is transmitted to the eNB 200.

The UE 100 that receives the WLAN measurement command performs the WLANmeasurement in accordance with the WLAN measurement command. Forexample, the UE 100 measures a received power of a beacon signal fromthe WLAN AP 300, and the like, for the WLAN identifier included in theWLAN measurement command.

In step S2, the UE 100 detects an event as a transmission trigger forthe WLAN measurement report, on the basis of the trigger informationincluded in the WLAN measurement command. Here, when the UE 100 istransitioned to an idle state, the UE 100 establishes again an RRCconnection with the eNB 200 in order to transmit the WLAN measurementreport to the eNB 200 (step S3).

In step S4, the UE 100 transmits the WLAN measurement report to report aresult of the WLAN measurement, to the eNB 200. The WLAN measurementreport includes a WLAN identifier and a WLAN measurement result(received power of a beacon signal, and the like), for example.

In step S5, the eNB 200 that receives the WLAN measurement reporttransmits, to the UE 100, a Steering command (offload command) toinstruct the execution of the offload, on the basis of the WLANmeasurement report, the load of RAN, and the like. It is noted that theSteering command may be a command to instruct a traffic transition(offload cancellation) from the WLAN to the eNB 200, in addition to acommand to instruct a traffic transition (offload) from the eNB 200 tothe WLAN.

In step S6, the UE 100 that receives the offload command executes anoffload. That is, the UE 100 switches so that the traffic to betransmitted and received to and from the eNB 200 is passed on to theWLAN AP 300. It is noted that when the UE 100 does not establishconnection with the WLAN AP 300 when the offload command is received,the UE 100 establishes connection with the WLAN AP 300 prior to theoffload.

In step S7, the UE 100 transmits, to the eNB 200, a response respondingto the offload command.

In such a sequence, when the eNB 200 selects a UE 100 subject tooffload, the selection of the UE 100 subject to offload may beinappropriate. The offload should not be performed for a UE 100 such asa UE 100 around which no WLAN AP 300 is present, a UE 100 which ismoving, or a UE 100 whose battery remaining amount is low.

In the first embodiment, when the UE 100 is selected as a targetterminal subject to offload in which traffic is transitioned to the WLANsystem, the UE 100 determines on the basis of a determination parameterrelated to the situation of the UE 100 whether or not the offload shouldbe performed. Detail of the determination parameter (a determinationparameter 1 to a determination parameter 4) will be described later.

When the UE 100 determines on the basis of the determination parameterthat the offload should not be performed, the UE 100 transmits arejection notification, to the eNB 200, related to rejection to theoffload. A timing to transmit the rejection notification to the eNB 200(an operation pattern 1 to an operation pattern 3) will be describedlater.

The eNB 200 excludes the UE 100 from a target terminal subject tooffload, when the UE 100 is selected as a target terminal subject tooffload in which traffic is transitioned to the WLAN system, and whenthe eNB 200 receives a rejection notification related to rejection tothe offload from the UE 100. Accordingly, it is possible to properlyselect a UE 100 subject to offload.

(2) Determination Parameter

It is possible to use at least one of the determination parameter 1 tothe determination parameter 4 below as the determination parameterdescribed above.

The determination parameter 1 is information indicating whether or not aWLAN AP 300 is present around the UE 100. For example, if the UE 100receives a beacon signal from a WLAN AP 300, then it may be consideredthat the WLAN AP 300 is present around the UE 100. Alternatively, whenthe UE 100 holds location information of a WLAN AP 300 (AP locationinformation), if difference between GNSS location information and APlocation information of the UE 100 (that is, distance) is small, then itmay be possible to consider that the WLAN AP 300 is present around theUE 100. The UE 100 determines on the basis of the determinationparameter 1 that the offload should not be performed, and transmits arejection notification when no WLAN AP 300 is present around the UE 100.Thus, it is possible to avoid a UE 100 in a state where it is impossibleto be offloaded from being selected as a UE 100 subject to offload.

The determination parameter 2 is information indicating whether or notthe UE 100 is moving. For example, if a change of GNSS locationinformation of the UE 100 per unit time is larger than a predeterminedamount, then it may be considered that the UE 100 is moving.Alternatively, if a handover frequency or a cell reselection frequencyper unit time of the UE 100 is larger than a predetermined frequency,then it may be possible to consider that the UE 100 is moving. The UE100 determines on the basis of the determination parameter 2 that theoffload should not be performed and transmits a rejection notificationwhen the UE 100 is moving. The UE 100 that is moving passes through thecoverage area of the AP 300 in a short time. Accordingly, when the UE100 that is moving is excludable from a target subject to offload, it ispossible to avoid an inefficient offload from being performed.

The determination parameter 3 is information indicating a batteryremaining amount of the UE 100. Information indicating a batteryremaining amount may be the voltage value of the battery 140 or an indexindicating the voltage level of the battery 140. The UE 100 determineson the basis of the determination parameter 3 that the offload shouldnot be performed and transmits a rejection notification when the batteryremaining amount falls below the threshold value. When an offload isperformed, the power consumption of the UE 100 increases, so that thereoccur problems that the UE 100 runs out of its battery, or that anoutgoing call (including an emergency call) becomes impossible, and thelike. Accordingly, when the UE 100 whose battery remaining amount issmall is excludable from a target subject to offload, it is possible toavoid such problems.

The determination parameter 4 is information indicating the powerconsumption level of the UE 100. For example, when the UE 100 is set toa power saving mode, the power consumption level of the UE 100 is small.When the UE 100 is set to a high performance mode, the power consumptionlevel of the UE 100 is large. The UE 100 determines on the basis of thedetermination parameter 4 that the offload should not be performed andtransmits a rejection notification when the power consumption levelexceeds the threshold value. When the offload is performed, the powerconsumption of the UE 100 increases, so that there are problems on theUE 100 whose power consumption level is high that the power consumptionexceeds an allowance because of the offload, and the like. Accordingly,when the UE 100 whose power consumption level is high is excludable froma target subject to offload, it is possible to avoid such problems.

(3) Operation Pattern 1

FIG. 8 is sequence diagram of an operation pattern 1 according to thefirst embodiment. Here, differences from a basic operation describedabove will be mainly described.

As shown in FIG. 8, in step S1, the UE 100 receives a WLAN measurementcommand indicating that the UE 100 is selected as a target terminalsubject to offload, from the eNB 200.

In step S10, the UE 100 determines on the basis of the determinationparameter whether or not an offload should be performed.

When the UE 100 determines that an offload should not be performed (stepS10: No), in step S11, the UE 100 transmits a rejection notification tothe eNB 200 as a response to the WLAN measurement command. The UE 100may include rejection reason information indicating a reason for therejection into the rejection notification. Examples of the reason forthe rejection include “no WLAN AP 300 is present in its neighborhood”,“the UE 100 is moving”, “the battery remaining amount is small”, and“power consumption level is high”. The eNB 200 which receives therejection notification excludes the UE 100 from a target terminalsubject to offload.

On the other hand, when the UE 100 determines that an offload should beperformed (step S10: Yes), the UE 100 detects an event to be atransmission trigger for a WLAN measurement report, on the basis oftrigger information included in the WLAN measurement command in step S2.The subsequent operations are similar to the basic operation describedabove.

(4) Operation Pattern 2

FIG. 9 is a sequence diagram of an operation pattern 2 according to thefirst embodiment. Here, differences from a basic operation describedabove will be mainly described.

As shown in FIG. 9, steps S1 to S3 are similar to the basic operationdescribed above.

In step S20, the UE 100 determines on the basis of the determinationparameter whether or not an offload should be performed.

When the UE 100 determines that an offload should not be performed (stepS20: No), in step S4′, the UE 100 transmits, to the eNB 200, a rejectionnotification together with the WLAN measurement report to report aresult of the WLAN measurement. The UE 100 may transmit the rejectionnotification included into the WLAN measurement report, and may transmitthe WLAN measurement report and the rejection notification by anindividual message. The UE 100 may include rejection reason informationinto the rejection notification. The eNB 200 which receives therejection notification excludes the UE 100 from a target terminalsubject to offload.

On the other hand, when the UE 100 determines that an offload should beperformed, the UE 100 transmits the WLAN measurement report to the eNB200, without transmitting the rejection notification. The subsequentoperations are similar to the basic operation described above.

(5) Operation Pattern 3

FIG. 10 is a sequence diagram of an operation pattern 3 according to thefirst embodiment. Here, differences from a basic operation describedabove will be mainly described.

As shown in FIG. 10, steps S1 to S5 are similar to the basic operationdescribed above. Specifically, in step S5, the UE 100 receives anoffload command to instruct the execution of an offload from the eNB200.

In step S30, the UE 100 determines on the basis of the determinationparameter whether or not an offload should be performed.

When it is determined that an offload should not be performed (step S30:No), in step S31, the UE 100 transmits a rejection notification to theeNB 200 as a response to the offload command. It is noted that, the UE100 may include rejection reason information into the rejectionnotification. The eNB 200 which receives the rejection notificationexcludes the UE 100 from a target terminal subject to offload.

On the other hand, when it is determined that an offload should beperformed (step S30: Yes), in step S6, the UE 100 executes the offload.The subsequent operations are similar to the basic operation describedabove.

Summary of First Embodiment

As described above, when the UE 100 is selected as a target terminalsubject to offload, the UE 100 determines on the basis of thedetermination parameter related to a situation of the UE 100 whether ornot an offload should be performed. When the UE 100 determines on thebasis of the determination parameter that the offload should not beperformed, the UE 100 transmits a rejection notification, to the eNB200, related to rejection to the offload. The eNB 200 excludes the UE100 from a target terminal subject to offload when the UE 100 isselected as a target terminal subject to offload, and when the eNB 200receives a rejection notification related to rejection to the offloadfrom the UE 100. Accordingly, it is possible to properly select a UE 100subject to offload.

In the operation pattern 1 according to the first embodiment, it ispossible to reduce the process load of the UE 100 and to reduce anamount of consumption of the radio resource involved in the WLANmeasurement report because the rejection notification is transmitted tothe eNB 200 without transmitting the WLAN measurement report to the eNB200. On the other hand, in the operation pattern 3 according to thefirst embodiment, because the UE 100 makes determination immediatelybefore a timing when the offload should be performed, it is possible toproperly make the determination on the basis of the latest situation ofthe UE 100. The operation pattern 2 according to the first embodimenthas a property intermediate that of the operation pattern 1 and that ofthe operation pattern 3.

Second Embodiment

A second embodiment will be described while focusing on the differencesfrom the first embodiment. A system configuration and a basic operationaccording to the second embodiment are similar to those in the firstembodiment.

Operation According to Second Embodiment

An operation according to the second embodiment is performed prior tothe basic operations described above. Specifically, the UE 100transmits, to the eNB 200, a terminal information notification includingthe determination parameter described above (at least one of thedetermination parameter 1 to the determination parameter 4) before theUE 100 is selected as a target terminal subject to offload. The terminalinformation notification may be “UE Capability Information” that is oneof RRC messages.

The eNB 200 receives the terminal information notification including thedetermination parameter from the UE 100 before the UE 100 is selected asa target terminal subject to offload. And, the eNB 200 selects the UE100 subject to offload on the basis of the determination parameter. Forexample, the eNB 200 excludes a UE 100, around which no WLAN AP 300 ispresent, from a target terminal subject to offload, on the basis of thedetermination parameter 1. The eNB 200 excludes a UE 100 which is movingfrom a target terminal subject to offload, on the basis of thedetermination parameter 2. The eNB 200 excludes a UE 100 whose batteryremaining amount falls below the threshold value from a target terminalsubject to offload, on the basis of the determination parameter 3. TheeNB 200 excludes a UE 100 whose power consumption level exceeds thethreshold value from a target terminal subject to offload, on the basisof the determination parameter 3.

FIG. 11 is a sequence diagram according to the second embodiment.

As shown in FIG. 11, in step 5101, the eNB 200 transmits, to the UE 100,a UE Capability Enquiry to request to transmit a terminal informationnotification (UE Capability Information).

In step 5102, the UE 100 which receives the UE Capability Enquiry,transmits, to the eNB 200, the terminal information notificationincluding the determination parameter (UE Capability Information).

Summary of Second Embodiment

As described above, the UE 100 transmits, to the eNB 200, the terminalinformation notification including the determination parameter beforethe UE 100 is selected as a target terminal subject to offload. The eNB200 receives the terminal information notification including thedetermination parameter from the UE 100 before the UE 100 is selected asa target terminal subject to offload. The eNB 200 selects a UE 100subject to offload on the basis of the determination parameter. Thus, itis possible to properly select a UE 100 subject to offload.

Other Embodiments

In the second embodiment described above, the eNB 200 selects a UE 100subject to offload, on the basis of the determination parameter receivedfrom the UE 100. However, the eNB 200 may select a UE 100 subject tooffload without relying on the determination parameter received from theUE 100. For example, the eNB 200 measures an elapsed time after a UE 100handovers to a cell of the eNB 200, excludes a UE 100 in which theelapsed time is shorter than a fixed time from a target terminal subjectto offload. Thus, it is possible to include a UE 100 which is in a cellof the eNB 200 in the long term as a target terminal subject to offload,and to exclude a UE 100 which only temporarily passes through the a cellof the eNB 200 from a target terminal subject to offload.

The second embodiment described above is assumed to be used togetherwith the first embodiment. However, the second embodiment may beexecuted separately from the first embodiment, and the second embodimentmay be executed independently.

In each of the embodiments described above, as one example of thecellular communication system, the LTE system is described, however, thepresent disclosure is not limiting to the LTE system, and the presentdisclosure may be applied to systems other than the LTE system.

In each operation sequence described above, an operation performed bythe eNB 200 (base station) may be operated by another network device(for example, an RNC) instead of the base station.

INDUSTRIAL APPLICABILITY

According to the present disclosure, it is possible to provide a userterminal with which it is possible to properly select a user terminalsubject to offload, a cellular base station therefor, and a processortherefor.

1. A user terminal comprising: a controller including at least oneprocessor and at least one memory, and configured to: receive an offloadcommand from a cellular base station, the offload command instructing anoffload, the offload being an operation in which the user terminalsteers traffic from the cellular base station to a wireless local areanetwork (WLAN) access point while maintaining a connection between theuser terminal and the cellular base station; attempt to connect to theWLAN access point in response to receiving the offload command; inresponse to failing in connecting to the WLAN access point, determinewhether a reason for the failure of connection to the WLAN access pointis a first reason or a second reason, the first reason being an issue ofa radio link between the user terminal and the WLAN access point, andthe second reason being an internal issue of the user terminal; andtransmit a failure indication to the cellular base station in responseto failing in connecting to the WLAN access point, the failureindication indicating that the user terminal fails in connecting to theWLAN access point, wherein the failure indication includes informationindicating whether the reason is the first reason or the second reason.2. The user terminal according to claim 1, wherein the controller isfurther configured to transmit a WLAN measurement report to the cellularbase station before receiving the offload command, the WLAN measurementreport including at least one WLAN identifier and measurement results ofreceived power of WLAN signals.
 3. A method for performing at a userterminal, comprising: receiving an offload command from a cellular basestation, the offload command instructing an offload, the offload beingan operation in which the user terminal steers traffic from the cellularbase station to a wireless local area network (WLAN) access point whilemaintaining a connection between the user terminal and the cellular basestation; attempting to connect to the WLAN access point in response toreceiving the offload command; in response to failing in connecting tothe WLAN access point, determining whether a reason for the failure ofconnection to the WLAN access point is a first reason or a secondreason, the first reason being an issue of a radio link between the userterminal and the WLAN access point, and the second reason being aninternal issue of the user terminal; and transmitting a failureindication to the cellular base station in response to failing inconnecting to the WLAN access point, the failure indication indicatingthat the user terminal fails in connecting to the WLAN access point,wherein the failure indication includes information indicating whetherthe reason is the first reason or the second reason.
 4. The methodaccording to claim 3, further comprising transmitting a WLAN measurementreport to the cellular base station before receiving the offloadcommand, the WLAN measurement report including at least one WLANidentifier and measurement results of received power of WLAN signals. 5.An apparatus for controlling a user terminal, comprising: at least oneprocessor and at least one memory, the at least one processor configuredto: receive an offload command from a cellular base station, the offloadcommand instructing an offload, the offload being an operation in whichthe user terminal steers traffic from the cellular base station to awireless local area network (WLAN) access point while maintaining aconnection between the user terminal and the cellular base station;attempt to connect to the WLAN access point in response to receiving theoffload command; in response to failing in connecting to the WLAN accesspoint, determine whether a reason for the failure of connection to theWLAN access point is a first reason or a second reason, the first reasonbeing an issue of a radio link between the user terminal and the WLANaccess point, and the second reason being an internal issue of the userterminal; and transmit a failure indication to the cellular base stationin response to failing in connecting to the WLAN access point, thefailure indication indicating that the user terminal fails in connectingto the WLAN access point, wherein the failure indication includesinformation indicating whether the reason is the first reason or thesecond reason.
 6. The apparatus according to claim 5, wherein the atleast one processor is further configured to transmit a WLAN measurementreport to the cellular base station before receiving the offloadcommand, the WLAN measurement report including at least one WLANidentifier and measurement results of received power of WLAN signals. 7.The user terminal according to claim 2, wherein the controller isfurther configured to transmit WLAN information to the cellular basestation in addition to transmitting the WLAN measurement report, theWLAN information indicating whether or not a WLAN access point withwhich the user terminal communicates is present around the userterminal.